In the aircraft industry the skin of an aircraft is traditionally riveted to frame members such as stringers or the like. Because of the large number of rivets utilized to produce a single aircraft, and also because of the requirements of virtually indefinite life of the rivets, much attention has been given in the industry to various methods and apparatus for riveting. One riveting method and apparatus which has been utilized by the industry for a number of years is shown in U.S. Pat. No. 3,557,442. This patent discloses the utilization of slug rivets to secure two members together, the workpieces which are to be joined together being initially clamped together. This patent teaches that the upper rivet forming anvil is initially extended to a full down locked position with all of the rivet upsetting force then being applied by upward movement of the lower rivet forming anvil, the ends of the rivet being simultaneously formed. Due to the sequential movement of the rams the surfaces of the workpieces will move relative to a fixed work plane. This is referred to in the industry as a "wink".
As the workpieces are winked or moved during the squeeze cycle of the foregoing process they will have a tendency to oscillate before returning to their original position. This oscillation could delay the next rivet forming operation or any other subsequent operation. Additionally, if the slug rivet can be formed without winking better control of the position of the slug can be achieved. As there would be no movement of the workpiece even greater uniformity of the bulging of the rivet may be achieved which is desirable for rivet fatigue life cycles. In addition, by not moving the workpieces during the riveting there is a potential for even faster rate times. In addition the workpieces can be rigidly fixtured thus eliminating the need for temporary fasteners that would have to be replaced.